This proposal is in response to the Biomedical Research Support Shared Instrument Grant request. The proposal consists of eight projects requiring the use of a high quality transmission electron microscope and accessories. Five of these projects have the current support from six U. S. Public Health Service research awards to five of the ten Co-Investigators. The other three projects are currently funded from other sources or are part of proposals pending review. The proposal establishes a need of the University of Maryland School of Dentistry for a high quality research transmission electron microscope and accessories to be placed in a core facility and made available to investigators with PHS support and to other investigators on a time available basis.